Experimental and numerical investigation of cylinder rising in co-current turbulent air pipe flow: Application in pneumatic ice drilling

Abstract

Air-reverse-circulation drilling into ice sheets is a promising clean technology for fast and safe ice sample recovery in the polar regions. However, a few studies in the literature explore an ice cylinder's rising from rest in tubing filled by co-current air flow. This study builds an experimental setup as well as uses the computational fluid dynamics (CFD) method to characterize the process of ice cylinder rising from being seated at bottom. Variations of the drag coefficient when a cylinder starts to rise and the critical velocity, i.e., the minimum air injection velocity to raise a cylinder, are investigated with the experiments and simulations. Reynolds number is found to have a marginal effect on the drag coefficient and critical velocity while ice-cylinder-pipe geometry can influence the two factors. Wall effect resulting from the existence of pipe lateral wall can enhance the drag coefficient and accordingly, reduce critical velocity. Decreasing the clearance between cylinder and pipe or increasing cylinder length is observed to strengthen the wall effect, but enlarging the cylinder diameter surprisingly weakens the wall effect. A mathematical correlation is developed to quantify the interplay between cylinder-pipe geometry and critical velocity by using parameters like sphericities and diameter ratio. When a cylinder continues to rise off bottom, its drag coefficient would first increase quickly and then decrease gradually to a value where terminal velocity is achieved.